kind of cool multiday event with with ways to unlock special content (characters in game) in the Endless series.
Endless Day requirements vary a little per title:
Endless Legend: starting a new game should lead to a new quest being offered after 2-3 turns - complete the quest, and you'll recruit the Endless Day hero, and unlock the achievement
Endless Space: you'll need to buy/recruit the new hero (Emlek Tarosh) in the usual manner; I think you may need to win the game with him to unlock the achievement, but I'm not certain
Dungeon of the Endless: start a game with Esseb in your party and get to level 4 to permanently unlock him; beat the game to unlock the achievement
Yup, just unlocked DotE character. Pretty painless. Not planning on beating the game this run though, I'm in the middle of Might & Magic Legacy X and would rather play that (already beat DotE recently and need something else for now).
I own Endless Space... but MMLX will prevent me from putting enough time into it to figure out what I need to do, as I've never played it before.
These achievements can only be unlocked during Endless Day event? How long will it take to unlock them?
This really depends.
I just unlocked the character for Dungeon of the Endless, but I've also beaten the game before. It probably took me about 30 minutes, give or take, and could probably be done in quite a bit less if you were playing it on a regular basis (and focusing only on getting to level 4 to unlock, so skipping any long term planning/prep).
But if you haven't played the game before? Good luck getting that achievement (beating the game). Though I suppose you could do it easier on 'very easy', though I'm not sure how much easier that actually makes the game. If you're new to the game you might beat it by the 25th, maybe.
I'm assuming the other two games have similar requirements -- a fairly easy challenge if you're up to speed with the game already, but quite a bit harder if you need to come up to speed with a new 4x game.
NOTE -- this shouldn't scare anyone away from Dungeon of the Endless... it's an absolutely fantastic game and I highly recommend it. That said, getting to the point where you can beat a roguelike like this is a time consuming process. I have my strategies worked out now, so it's manageable, but I determined those strategies on the backs of quite a few stupid deaths.